The Present invention relates generally to disk brakes and more particularly to disk brakes which employ a plurality of rotors or disks slidably mounted relative to a fixed caliper.
One of the inherent problems associated with conventional disk brakes is that the required clamping loads are quite high for a given torque. To generate such clamping loads requires massive calipers. The size of these calipers necessitates the use of disks or rotors of reduced diameter. The high clamping loads similarly dictate the use of large diameter cylinders within the calipers and coupled with the deflection of the caliper create a brake having a "spongy" feel. In addition, the high clambing loads generate increased heat; conventional disk brakes use a large amounts of metal to dissipate the heat and are therefore heavier than a drum brake equivalent.
The principal advantage of the dual disk brakes is lower clamping loads. The effect of the lower clamping loads permits a reduction in the weight and perhaps the cost of the dual disk brake. A pronounced problem of the prior dual disk brakes is that they have tended to bind or brinnel on their hub and are prone to rattle.
In the preferred embodiment of the invention, a plurality of annular shaped rotors are splined to a disk hub. The plurality of rotors present increased surface areas which distributes heat quickly, thus proportionately reducing lining temperature and providing for faster fade recovery. More specifically, the splined design of one embodiment of the present invention includes a plurality of grooves formed in a disk hub and a like plurality of teeth formed in each of two rotors. In another embodiment of the invention the teeth are formed on the disk hub and the grooves are formed in the rotors. A hardened stainless steel liner is placed in a groove and receives a corresponding tooth in a manner to distribute the load from the tooth throughout the relatively soft disk hub. This liner is arcuately shaped and includes a deformable wall to absorb torque and to cushion the rotor. At very high torque levels this deformable wall bottoms out, which enhances the distribution of forces onto the disk hub. In one embodiment these liners have a loaded flat side and a curved side which loads the disk in a direction to reduce the amount of "squirming" during braking. Another embodiment uses rotor teeth with parallel sides. In this way the rotor is located only by the sides of the teeth as they are biased into the disk hub and not by the bottom of the groove, thereby allowing for greater thermal expansion without loss of guidance. By utilizing the sliding dual rotor configuration of the present invention, several options are available regarding the construction of the caliper housing. One of these options is to use a stamped steel caliper bridge. This is possible because the clamping loads generated between the caliper and each rotor are reduced by a factor of two (2). Further, it first should be noted that the in the present invention the caliper can be fixedly mounted to the steering knuckle as opposed to prior designs that require the caliper to absorb torque while being slideable attached to the steering knuckle.
One important characteristic of a brake is fluid stiffness, that is, the volume of fluid that has to be added (or deleted) to change applied torque by a given amount. This fluid stiffness is affected by the rigidity or structural stiffness of the caliper, this is as the caliper deflects more or less fluid, as the case may be, is needed to change the applied torque. In the present invention the piston area can be half that of a single disk design so the bridge of the caliper could be made half as stiff in order for the overall stiffness of the system to be the same. In actual practice, the twin disk design is generally 30 percent to 50 percent stiffer than conventional brakes. A counter factor presented by dual disk brakes is that the total pad compression may be increased since four (4) pads are used in series instead of two (2). In actual practice, however, since the total pad area is greater, the thickness can be reduced, offsetting this effect.
In addition, generally the total friction material required in a brake is determined by wear characteristics and the desired life. In the present twin disk brake, since brake effort is divided between four (4) pads, each pad will exhibit one-half the wear per pad (when compared to two pad brakes). Consequently, operating temperatures are lowered and wear is reduced. Therefore, it is reasonable that the lining material used in the present invention could be one-half the thickness of a conventional brake.
Accordingly, the preferred embodiment of the invention comprises: a disk brake including a disk hub adapted to be mounted to a wheel, a plurality of annular rotors or disks, means for mounting the rotors to the disk hub such that the rotors rotate with disk hub and are free to slide in a first direction substantially perpendicular to the direction of rotation, a plurality of opposing situated brake pads, one associated with each rotor and means for urging the brake pads into sequential frictional engagement with the rotors. Specially shaped liners interpose grooves in the disk hub and teeth on each rotor. A second set of liners is fitted between a caliper bridge and the plurality of brake pads to enhance sliding and reduce friction.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.